/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

package javax.servlet.jsp.tagext;

/**
 * Optional class provided by the tag library author to describe additional
 * translation-time information not described in the TLD.
 * The TagExtraInfo class is mentioned in the Tag Library Descriptor file (TLD).
 * <p>
 * <p>
 * This class can be used:
 * <ul>
 * <li> to indicate that the tag defines scripting variables
 * <li> to perform translation-time validation of the tag attributes.
 * </ul>
 * <p>
 * <p>
 * It is the responsibility of the JSP translator that the initial value
 * to be returned by calls to getTagInfo() corresponds to a TagInfo
 * object for the tag being translated. If an explicit call to
 * setTagInfo() is done, then the object passed will be returned in
 * subsequent calls to getTagInfo().
 * <p>
 * <p>
 * The only way to affect the value returned by getTagInfo()
 * is through a setTagInfo() call, and thus, TagExtraInfo.setTagInfo() is
 * to be called by the JSP translator, with a TagInfo object that
 * corresponds to the tag being translated. The call should happen before
 * any invocation on validate() and before any invocation on
 * getVariableInfo().
 * <p>
 * <p>
 * <tt>NOTE:</tt> It is a (translation time) error for a tag definition
 * in a TLD with one or more variable subelements to have an associated
 * TagExtraInfo implementation that returns a VariableInfo array with
 * one or more elements from a call to getVariableInfo().
 */

public abstract class TagExtraInfo {

	// zero length VariableInfo array
	private static final VariableInfo[] ZERO_VARIABLE_INFO = {};
	// private data
	private TagInfo tagInfo;

	/**
	 * Sole constructor. (For invocation by subclass constructors,
	 * typically implicit.)
	 */
	public TagExtraInfo() {
		// NOOP by default
	}

	/**
	 * information on scripting variables defined by the tag associated with
	 * this TagExtraInfo instance.
	 * Request-time attributes are indicated as such in the TagData parameter.
	 *
	 * @param data The TagData instance.
	 * @return An array of VariableInfo data, or null or a zero length array
	 * if no scripting variables are to be defined.
	 */
	public VariableInfo[] getVariableInfo(TagData data) {
		return ZERO_VARIABLE_INFO;
	}

	/**
	 * Translation-time validation of the attributes.
	 * Request-time attributes are indicated as such in the TagData parameter.
	 * Note that the preferred way to do validation is with the validate()
	 * method, since it can return more detailed information.
	 *
	 * @param data The TagData instance.
	 * @return Whether this tag instance is valid.
	 * @see TagExtraInfo#validate
	 */

	public boolean isValid(TagData data) {
		return true;
	}

	/**
	 * Translation-time validation of the attributes.
	 * Request-time attributes are indicated as such in the TagData parameter.
	 * Because of the higher quality validation messages possible,
	 * this is the preferred way to do validation (although isValid()
	 * still works).
	 * <p>
	 * <p>JSP 2.0 and higher containers call validate() instead of isValid().
	 * The default implementation of this method is to call isValid().  If
	 * isValid() returns false, a generic ValidationMessage[] is returned
	 * indicating isValid() returned false.</p>
	 *
	 * @param data The TagData instance.
	 * @return A null object, or zero length array if no errors, an
	 * array of ValidationMessages otherwise.
	 * @since 2.0
	 */
	public ValidationMessage[] validate(TagData data) {
		ValidationMessage[] result = null;

		if (!isValid(data)) {
			result = new ValidationMessage[]{
					new ValidationMessage(data.getId(), "isValid() == false")};
		}

		return result;
	}

	/**
	 * Get the TagInfo for this class.
	 *
	 * @return the taginfo instance this instance is extending
	 */
	public final TagInfo getTagInfo() {
		return tagInfo;
	}

	/**
	 * Set the TagInfo for this class.
	 *
	 * @param tagInfo The TagInfo this instance is extending
	 */
	public final void setTagInfo(TagInfo tagInfo) {
		this.tagInfo = tagInfo;
	}
}

